1. Field of Invention
The present invention relates to syringes, and more particularly to a syringe with plunger anti-detachment mechanism which securely locks up the plunger in the hollow barrel after use for preventing the plunger detaching from the hollow barrel accidentally, so as to prevent the used needle from contacting with anybody.
2. Description of Related Arts
It is well known that the needles of syringes are frequently intended for disposal after single use and rendered inoperative to prevent accidental injury or re-use with the substantial risk cross-contamination.
There are many conventional syringes employed with a needle retraction device which enables the used needle being retracted inside the barrel. For example, U.S. Pat. Nos. 4,650,468 and 4,804,370 each suggests a kind of medical syringe that enables its used needle being retracted inside the barrel by re-pulling out the plunger. U.S. Pat. No. 4,695,274 discloses an improved kind of medical syringe which further includes a spring inside so as to retract the needle inside the barrel.
U.S. Pat. No. 6,206,857 which is invented by the applicant of the present invention provides a syringe with needle retraction arrangement for automatically retracting the hollow needle into a hollow plunger after use that prevents the used needle from contacting with anybody. Moreover, the ""857 patent is easy to assembly and has a relatively low manufacturing cost while no air ventilation holes or air space is required in the structure.
However, when the used needle is retracted inside the barrel, the used needle may be exposed if the plunger is accidentally detached from the barrel. Moreover, there is no guarantee that the used syringe will not be re-used by simply replacing the used needle from the barrel with another set of plunger and needle.
Therefore, some conventional syringe may comprises a locking device in order to lock up the plunger with the barrel, so as to prevent the plunger from being detached from the barrel accidentally. However, the locking device has a major drawback.
In order to fill the liquid form medicine in the barrel, a pulling force must be applied on the plunger to pull the plunger away from the hollow needle, so as to suck the medicine into the barrel through the needle. When the plunger is pushed towards to the needle gradually, the medicine is pushed to eject through the needle which penetrated into a patient""s tissue. Therefore, the sucking operation and the ejecting operation require opposed pulling and pushing forces on the plunger with respect to the barrel. However, the locking device may lead to different operational results since the locking device may lock up the plunger during the sucking operation or even during the ejecting operation. Any unwanted operation of the locking device will cause a serious injury to the patient. However, it is unreasonable that the syringe utilizes a complicated locking device to achieve a safety and precise operation thereof, which may largely increase the number of parts and the manufacturing cost and labor, since the syringe is specifically designed for disposable one-time use.
In view of above, conventional syringes have drawback in practical use, and hence there has been a demand for a syringe with a locking device which is improved in both safety and operability.
The main object of the present invention is to provide a syringe with plunger anti-detachment mechanism which locks up the plunger in the hollow barrel after use For preventing the plunger detaching from the hollow barrel accidentally.
Another object of the present invention is to provide a syringe with plunger anti-detachment mechanism which can guarantee the syringe will not be re-used since the used needle is permanently locked in the barrel. Therefore, the syringe is well suited for disposable one-time use.
Another object of the present invention is to provide a syringe with plunger anti-detachment mechanism which does not affect the sucking operation and the ejecting operation of the syringe so as to prevent the plunger being stuck in a mid-way of the operation with respect to the barrel accidentally.
Another object of the present invention is to provide a syringe with plunger anti-detachment mechanism wherein the hollow needle is automatically retracted into the hollow plunger after use so as to prevent the used needle from contacting with anybody.
Another object of the present invention is to provide a syringe with plunger anti-detachment mechanism which is easy to assembly and has a relatively low manufacturing cost.
Accordingly, in order to accomplish the above objects, the present invention provides a syringe, which comprises:
a hollow barrel having an open end portion, a needle mounting portion, a tubular needle hub extending from the needle mounting portion to provide a needle passageway therethrough;
a hollow needle having a tissue penetrating end and a tip end thereof affixed with a cylindrical tip head, wherein the tip head of the hollow needle is disposed in the needle mounting portion with the tissue penetrating end penetrating through the needle passageway;
a mounting seat integrally affixed within the needle mounting portion of the hollow barrel for securely mounting the tip head of the hollow needle in position;
a hollow plunger adapted to travel through the hollow barrel, the hollow plunger having an outer closed end and an inner end inserted in the hollow barrel through the open end portion of the hollow barrel;
a needle retraction arrangement disposed in the hollow barrel for retracting the hollow needle into the hollow plunger; and
a plunger anti-detachment mechanism, comprising:
at least a locking stopper radially provided at an inner annular wall of the hollow barrel; and
at least a resilient arm, having a locking latch outwardly extended therefrom, radially extended from the hollow plunger wherein the locking latch of the resilient arm is adapted to normally slide along an inner annular wall of the hollow barrel until the locking latch is extended to the locking stopper so as to block up an axial movement of the hollow plunger with respect to the hollow barrel, so that the hollow plunger is interlocked with the hollow barrel to retain the hollow needle in the hollow plunger.